1. Field of the Invention
This invention relates to additives for lubricating oils, particularly to detergents comprising sulfurized overbased phenates, an oil industry term for compounds which are generally alkaline earth metal alkyl phenolates.
2. Information Disclosure Statement
Sulfurized overbased phenate detergents are a common component used in motor oils. Currently, most of the overbased sulfurized products are manufactured using ethylene glycol. Not only is the process lengthy, but the product also contains undesirable ethylene glycol residue. In the case of the existing processes using methanol solvents, a petroleum sulfonate is required as a co-surfactant to assist in the overbasing of phenates.
U.S. Pat. No. 4,744,921 and British Patent GB 2,197,336 disclose methods for preparing Group II metal overbased sulfurized alkylphenols with elemental sulfur, including the use of a sulfurization catalyst, in solvents containing an inert hydrocarbon, an alkanol of at least 8 carbon atoms and a C.sub.2 -C.sub.4 alkylene glycol. Similarly, the abstract (CA96(26):220373w) of Czech patent CS 190767B discloses a process for preparing lubricating oil additives containing colloidally dispersed CaCO.sub.3 by treating alkyl or arylalkylphenolates (also known as phenates) with elemental sulfur and carbonating the product in the presence of Ca(OH).sub.2.
U.S. Pat. No. 4,100,085 describes the use of ammonia or ammonium hydroxide as a promoter in the synthesis of overbased sulfurized alkylphenols. Likewise, U.S. Pat. No. 4,212,752 describes the use of certain amino promoters, such as primary and secondary alkylamines, polyalkyleneamines, amino acids, etc., in the synthesis of overbased sulfurized alkylphenols.
One method of preparing Group II metal overbased sulfurized alkylphenols is described in U.S. Pat. No. 3,178,368 where an alkylphenol, a sulfonate, a high molecular weight alcohol lubricating oil and sulfur are combined and heated with agitation. Hydrated lime is then added, the system heated and ethylene glycol added. Water of reaction is removed, the mixture cooled, and carbon dioxide added. Uncombined CO.sub.2 is removed and the reaction vessel is heated to remove ethylene glycol, water and the high molecular alcohol. The product is overbased by the incorporation therein of hydrated lime and carbon dioxide.
U.S. Pat. No. 3,367,867 discloses a similar process to that of U.S. Pat. No. 3,178,368 with the exception that this patent discloses that the use of alkyl groups on the alkylphenol which are mixtures of straight and branched-chained alkyl results in products having suitable viscosities as well as antifoaming properties.
Basic sulfurized calcium alkylphenates are used as compounding agents or additives in lubricating oils to neutralize harmful acids in internal combustion engines and to inhibit corrosion, gum formation and piston ring sticking caused by oxidation of the lubricating oil and oxidative polymerization of the engine fuel residues Metal sulfonates are commonly used in lubricating oil compositions as additives, rust inhibitors and detergents It is highly desirable for such phenates or sulfonates to provide neutralization capacity for acids formed in engine combustion without too rapid a loss in alkalinity. In some cases, these compounding agents or additives are overbased, containing a molar excess of base over that needed to neutralize the phenolic material or sulfonic acid.
A problem associated with the preparation of overbased additive compounds is that of the incompatibility of the mixture of the alkaline earth metal phenate and the sulfonate as a final product The overbased materials, generally an alkaline earth metal compound, e.g. a carbonate, are dispersed by the phenate and/or sulfonate surfactant in the alkaline earth metal dispersing agent (i.e., the oil), the amount of dispersed alkaline earth metal being known as the overbased amount. Since the greater the basicity of the material the better, as this allows smaller amounts of the material to be used for a given effect in a lubricant, a greater degree of overbasing is highly desirable. However, to increase basicity, it is generally necessary to increase the dispersed alkaline earth metal content of the carbonate complex. The incompatibility problems of the phenate and sulfonate components are generally exacerbated by greater degrees of overbasing.
Overbased phenates, including sulfurized phenates, are commonly manufactured in the presence of ethylene glycol which must be removed from the product. The presence of glycol in overbased phenates can cause engine varnish or lacquer. Phenates are generally the reaction product of phenol or substituted phenol with a metal or ammonium base. Often the metal base is a Group II metal compound. Substituted phenols are generally mono-, di- or tri-hydrocarbyl substituted, such as alkyl, alkenyl, aryl, arylalkyl, or alkylaryl. The hydrocarbyl groups can comprise low molecular weight groups such as methyl, ethyl, the isomers of propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and the like up to high molecular weight materials having a number average molecular weight of 1000 or more. These hydrocarbyl substituents can be intermediate molecular weight polymer olefins such as C.sub.8 -C.sub.100 ethylene or propylene or butylene polymers The hydrocarbyl can be substituted with groups such as chlorine, bromine, hydroxy, nitro or sulfonic acid groups so long as such substitution does not interfere with the utility of the composition. The Group II metal compound can comprise a metal oxide, hydroxide, alcoholate, acetate and the like. Common metals are calcium, barium, strontium and magnesium. Often, the metal compound is calcium oxide or hydroxide. Phenates can contain sulfur which can be introduced by the reaction of elemental sulfur or SCl.sub.2 with phenol or substituted phenols, or by the reaction of elemental sulfur or SCl.sub.2 with metal phenates.
Methods of making these various phenates and sulfur-containing phenates and overbasing can be found in U.S. Pat. Nos. 2,680,096; 3,036,971; 3,178,368; 3,336,224, 3,437,595; 3,464,970; 3,761,414; 3,801,507; 3,810,837; 3,923,670; 3,932,289; 3,953,519; 3,966,621 and 3,969,233.
Oil soluble overbased sulfonates are made by reacting a base with oil-soluble sulfonic acids. Suitable oil-soluble sulfonic acids can be aliphatic or aromatic compounds. Suitable aromatic sulfonic acids are the oil-soluble petroleum sulfonic acids, commonly referred to as "mahogany acids," aryl sulfonic acids, and alkylaryl sulfonic acids. Illustrative of such sulfonic acids are dilauryl benzene sulfonic acid, lauryl cetyl benzene sulfonic acid, paraffin-substituted benzene sulfonic acids, polyolefin alkylated benzene sulfonic acids, such as polybutylene alkylated benezene sulfonic acids in which the polybutylene substituents have a molecular weight within the range of from about 100 to about 1000 and polypropylene alkylated benzene sulfonic acids in which the polypropylene substituents have a molecular weight within the range of from about 80 to about 1000. Examples of other suitable sulfonic acids are alpha-olefin benzene sulfonic acids, diparaffin wax-substituted phenol sulfonic acids, acetylchlorobenzene sulfonic acids, cetyl-phenol disulfide sulfonic acids, cetyl-phenol monosulfide sulfonic acids, and cetoxy capryl benzene sulfonic acids. Other suitable oil-soluble sulfonic acids are well described in the art, such as, for example U.S. Pat. No. 2,616,604; U.S. Pat. No. 2,626,207; and U.S. Pat. No. 2,767,209; and others.
Non-aromatic sulfonic acids are generally made by the sulfonation of any suitable aliphatic hydrocarbon such as alkanes, alkenes, and the like. Also, the hydrocarbyl groups may contain various substituents which do not interfere with later reactions or end use. One preferred group of non-aromatic sulfonic acids is made by the sulfonation of polymers, or copolymers, such as polymerized or copolymerized olefins.
The term "polymer olefins" as used herein refers to amorphous polymers and copolymers derived from olefinically unsaturated monomers. Such olefin monomers include olefins of the general formula RCH.dbd.CH.sub.2, in which R comprises hydrogen or an aliphatic or cycloaliphatic group of from 1 to about 20 carbon atoms, for example, propene, isobutylene, butene-1, 4-methyl-1-pentene, decene-1, vinylidene, norbornene, 5-methylene-2-norbornene, etc. Other olefin monomers having a plurality of double bonds may be used, in particular diolefins containing from about 4 to about 25 carbon atoms, e.g., 1,4-butadiene, 2,3-hexadiene, 1,4-pentadiene, 2-methyl-2,-5-hexadiene, 1,7-octadiene, etc. These polyolefins have number average molecular weights from about 36 to about 1000. Of these materials, a preferred group is polyethylene or polypropylene or polybutylene polymers. The olefin may be a copolymer, such as an ethylene propylene copolymer or ethylene-propylene-hexadiene terpolymer, or others.
The preparation of the sulfonic acids is well known. Such sulfonic acids can be prepared by reacting the material to be sulfonated with a suitable sulfonating agent, such as concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid or sulfur trioxide for a period of time sufficient to effect sulfonation, and thereafter separating insoluble acid sludge from the oil-soluble sulfonic acid. Overbased sulfonates are commonly made by the reaction of sulfonic acid with metal bases such as the oxide or hydroxide of calcium, magnesium or barium. In some cases, the sulfonate can be made from the metal itself or a derivative of said metal. Suitable processes for making overbased sulfonates are described in U.S. Pat. Nos., 3,126,640; 3,492,230; 3,524,814; and 3,609,076.
U.S. Pat. No. 4,412,927 teaches the preparation of detergent-dispersant compositions useful as additives for lubricating oils having a base of alkylbenzene sulfonates and sulfurized alkylphenates. The process employs sulfurized alkylphenates, alkaline-earth metal alkylbenzene sulfonates, alkylene glycols and carbon dioxide. The process requires carbonating at a temperature between about 100.degree. C. and 250.degree. C., a reaction medium comprising a sulfurized alkylphenate of an alkaline earth metal of a total basic number (TBN) (ASTM Standard D-2896) of between 0 and 170, the said alkylphenate having one or more C.sub.6 -C.sub.60 alkyl substituents, an alkaline earth metal alkylbenzene sulfonate of a molecular weight of more than about 300 and a TBN of less than or equal to about 150, an alkaline earth metal compound, an alkylene glycol and a diluent oil. The alkylene glycol is subsequently removed and the metallic detergent-dispersant is separated.
As is well-known, calcium phenates having TBN's of 80-250 tend to interact with low and high base sulfonates to produce haze and sediment when blended into crankcase oils. This phenate-sulfonate incompatibility can be influenced by the components in a finished oil. For example, the simultaneous presence of zinc dialkyldithiophosphate (ZnDTP) and water can aggravate the phenate-sulfonate interaction. Many finished oils contain ZnDTP. This phenate-sulfonate incompatibility is worsened when the finished oil contains a small amount of water, as can happen during handling and storage.
It has long been known, as evidenced by the preceding recital of the prior art, i.e., U.S. Pat. No. 4,412,927, that an overbased metallic detergent-dispersant can be prepared by carbonating a sulfurized alkylphenate of an alkaline earth metal having a TBN of between 0 and 170 (i.e., generally from about 80 to 170) with a cosurfactant such as an alkaline-earth metal alkylbenzene sulfonate having a molecular weight of more than 300 and a TBN of less than or equal to 150, an alkaline-earth metal compound, an alkylene glycol and a diluent oil. The resulting product requires removal of the alkylene glycol which can waste raw materials. Incomplete removal of the alkylene glycol can cause engine varnish.
In addition to the polyalkylene glycols commonly used in processes for the preparation of overbased sulfurized phenates, numerous other solvents or mixtures thereof have been used in the various stages of such processes. For example, U.S. Pat. No. 4,016,093 discloses the use of solvents including various combinations of mineral oil, monochlorobenzene and methanol for different stages of the processes. U.S. Pat. No. 3,933,289 discloses the use of C.sub.1 to C.sub.3 alkanols as the solvent for a process in which a magnesium alkoxide is formed, carbonated, sulfurized with elemental sulfur and then overbased. U.S. Pat. No. 2,916,454 discloses the use of benzol (benzene) as the solvent for sulfurization of alkylphenols with sulfur dichloride.
U.S. Pat. No. 2,785,131 discusses the use of low-boiling solvents including carbon disulfide, ethylene dichloride and hexane, and discloses the use of saturated mineral lube oils in the absence of such solvents for the sulfurization of alkylphenols with sulfur chlorides. In U.S. Pat. Nos. 2,518,379 and 2,480,664 the process of overbasing alkylated phenols which have been sulfurized with sulfur is reportedly improved by the addition of higher alcohols (such as stearyl, lauryl or cetyl) to the mineral oil solvent. U.S. Pat. No. 2,406,041 discloses the use of mineral oil solvents containing higher aliphatic alcohols or aliphatic nitriles.
U.S. Pat. No. 2,472,517 discloses the process of sulfurizing alkylphenols with sulfur dichloride in solvents such as aromatic or aliphatic hydrocarbons, carbon tetrachloride or chloroform. U.S. Pat. No. 2,399,878 discloses the use of solvents such as dichloroethane, chloroform, petroleum naphtha and benzol (benzene) in the sulfurizing of alkylphenols with sulfur dichloride. U.S. Pat. No. 2,800,451 discloses processes including the sulfurization of alkylphenols with sulfur dichloride in a solvent including hexane and a mixture of C.sub.10 -C.sub.18 alcohols.
U.S. Pat. No. 4,614,602 discusses various processes for producing overbased sulfurized phenates and discloses processes for reacting a sulfurized alkaline earth metal phenate with an alkaline earth metal alkylbenzene sulfonate in a "co-synthesis reaction" in the presence of a C.sub.1 -C.sub.4 alcohol In Example XXX, a mixture of xylenes and methanol is used as the solvent in the neutralization and overbasing steps.
None of the patents discussed above suggest that it would be advantageous to employ mixed solvents comprising aliphatic hydrocarbons and lower alkanols in the overbasing of metal phenates which have been sufurized with sulfur halides.